Field of the Invention
The present invention relates to a fuel cell stack.
Background Art
A proton exchange membrane fuel cell (PEMFC) is configured by stacking a membrane electrode assembly (MEA) and a separator. The MEA includes an electrolyte film formed of an ion-exchange membrane, an electrode formed of a catalytic layer which is arranged on one surface of the electrolyte film (an anode, and a fuel electrode), and an electrode formed of a catalytic layer which is arranged on the other surface of the electrolyte film (a cathode, and an air electrode).
The separator includes a fuel gas passage for supplying fuel gas (hydrogen) to the anode, an oxidation gas passage for supplying oxidation gas (oxygen, and in general, air) to the cathode, and a cooling medium passage for flowing through a cooling medium in a power generation region. The separator includes a fuel gas manifold, an oxidation gas manifold, and a cooling medium manifold in a non-power generation region.
A cell module is configured by superposing the MEA and the separator, a cell stacked body is configured by stacking the cell modules, terminals, end plates, and the like are arranged on both ends of the cell stacked body in a cell stacking direction, and the end plates on both of the ends are fastened to a fastening member (for example, a tension plate, a tension bolt, or the like) extending in the cell stacking direction on the outside of the cell stacked body, and thus a fuel cell stack is configured.
In the proton exchange membrane fuel cell, a reaction of converting hydrogen into hydrogen ions and electrons is performed on the anode side, the hydrogen ions are moved to the cathode side through the electrolyte film, and a reaction of generating water from oxygen, hydrogen ions, and electrons (electrons generated in an anode of the adjacent MEA pass through the separator, or electrons generated in an anode of a cell on one end of the cell stacked body flow to a cathode of a cell on the other end of the cell stacked body through an external circuit) is performed on the cathode side.
Anode Side: H2→2H*+2e−
Cathode Side: 2H*+2e−+(½)O2→H2O
When the separator is formed of metal, corrosion occurs in the cooling medium manifold of several cells on a high potential side (+side). It is assumed that this is because in the cooling medium manifold of the stacked cells, for example, when the separator is formed of SUS, Fe ions are eluted on a + electrode side, and OH ions are generated on a − electrode side, and thus Fe(OH)2 is generated (refer to FIG. 7). In addition, the amount of corrosion occurring is indicated by a corrosion current, and it is assumed that the corrosion occurs at a high potential side (refer to FIG. 8). When the corrosion progresses, the sealing reliability of the cell decreases. In addition, it is dangerous since electrolysis may occur in the stack according to high electroconductivity of the cooling medium. In addition, even in a reactant gas manifold (the fuel gas manifold, and the oxidation gas manifold), corrosion may occur by the same mechanism as that in the cooling medium manifold.
In order to solve the problem of the corrosion in the separator, a fuel cell stack including a sacrificial member is known (for example, Patent Document 1 described below). In Patent Document 1 described below, a fuel cell stack is disclosed in which a sacrificial member using a material which is less noble than that of a separator is arranged between the separator and a positive electrode terminal, and thus corrosion in the separator is suppressed.